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Karl Lashley: Theories & Contributions to Behaviorism

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  • 0:03 Recalling a Stranger's Name
  • 0:48 The Engram
  • 1:27 The Law of Mass Action
  • 2:19 Equipotentiality
  • 3:35 Lesson Summary
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Lesson Transcript
Instructor: Gaines Arnold

Gaines has a Master of Science in Education.

Karl Lashley was a neuropsychologist responsible for essential advances in scientific knowledge of brain function and memory. This lesson looks at his theory of mass action and the experimentation that led to the discovery of equipotentiality.

Recalling a Stranger's Name

A stranger passes you at a party, and you know you've seen her before. Some unique lilt of her voice or physical mannerism has triggered your memory and, though you cannot remember her name, you are convinced that you know her. It is a puzzle that absorbs you until finally something clicks and the name appears as if it were written in a book. Of course, that's Kathy somebody, but where do you know her from? You figuratively riffle through mental files until it starts to come back. She was a neighbor who moved to the city about five years ago. After that, the memories come flooding in and you walk over to say hi. How this happens was explained by a neuropsychologist named Karl Lashley.

The Engram

Memory has been a conundrum that many scientists have gone to great lengths to solve. Some, such as Descartes, simply philosophized regarding its essence, but opinion does not make for reliable research. In the twentieth century, a researcher by the name of Richard Semon posited that memory was stored in physical capacitors called engrams. Semon believed that these storage tanks were depositories into which memories were dropped until they were needed. The problem with Semon's theory, though, was that no one had ever located an engram in the brain. Karl Lashley searched diligently during his experiments with mice and that led him to a discovery that changed the way people understood memory.

The Law of Mass Action

The cerebral cortex is the complex portion of the brain whose size separates humans from other animals. It is the seat of reasoning and memory. Lashley conducted experiments with rats, trying to find the Semon's engram, but instead discovered that memory was not contained in single structures within the cortex.

Lashley worked with rats in a maze to understand how memory actually occurred. He would train a rat to run a maze and then he would cut away a piece of the cerebral cortex. Each time he did this, with different subjects, he found that the memory was impaired (the rat could no longer negotiate the maze). After many repetitions he learned that the entire cerebral cortex was involved in memory. This mass action was demonstrated by the rats in that it did not matter what part of the cortex was cut, the rat's memory was affected. However, cutting away parts of rats' brains led Lashley to an even more important discovery.

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